Life in the early universe

  • #26
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This is something I did not know. What should I make of the SETI project then? totally hopeless?

Also, do you think Carl Sagan was unaware of this when he wrote 'Contact'? the plot premise is that a machine in orbit around Vega receives pretty much the earliest radio broadcast powerful enough to escape the ionosphere.

He had another idea on how to say 'I'm here' - to seed a star with a huge amount of rare metals to give it a totally unnature absorption spectrum. Probably even more impossible, though.
impossible to filter it from the interstellar hydrogen noise.
 
  • #27
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impossible to filter it from the interstellar hydrogen noise.
This is what I thought too earlier today while on the train. If our radio signals are actually that weak, they would be drowned out by any random nearby cloud of gas that's a lot closer.

Or were you referring to the spectral absorption line characteristic?
 
  • #28
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This is what I thought too earlier today while on the train. If our radio signals are actually that weak, they would be drowned out by any random nearby cloud of gas that's a lot closer.

Or were you referring to the spectral absorption line characteristic?
yep i meant to say that artificial radio signals will be easily drowned out by interstellar noise.
 
  • #29
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H2Bro, did you know that if a radio signal was sent from Alpha Centauri, the nearest star system, with a signal strength equal to our most powerful transmitters, we wouldn't be able to receive it with our largest dishes? It would be so weak as to be undetectable.
Can you point me to a reference for that? Using Aricebo's radar dish, I get a signal of 20 mJy at alpha centauri. That's well within our ability to detect.
 
  • #30
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Can you point me to a reference for that? Using Aricebo's radar dish, I get a signal of 20 mJy at alpha centauri. That's well within our ability to detect.
I'd have to find it. I just remember reading it a while back. It's possible I am mistaken.
I tried doing the math before I posted, but couldn't figure out how to calculate it.
 
  • #31
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H2Bro, did you know that if a radio signal was sent from Alpha Centauri, the nearest star system, with a signal strength equal to our most powerful transmitters, we wouldn't be able to receive it with our largest dishes? It would be so weak as to be undetectable.
The VLT looked for signals from some exoplanet recently. I checked the numbers, we would have been able to detect signals similar to some of our transmissions in the past.


Also optical signalling methods would not work, even UV lasers, because the star's glare would totally wipe it out and the angular divergence would be unresolvable.
Humans can outshine sun with a very narrow frequency band (like 1 Hz) and high-power lasers (or multiple lasers) - it is expensive, but possible with current technology. However, you have to know the specific frequency and the radial velocity between sender and receiver to see the signal.



An old post:
3) However, the most discouraging SETI statistic has to be the fact that our own gloriously human friendly cosmological situation is a statistical rounding error of about .000,001. In five billion years, we have managed to accumulate one single mathematically capable species descended from nothing more then a few hundred breading pairs.
If (on average) 1 out of 1 billion species develops intelligence on a human level and an average planet with life sees 1 billion species during the lifetime of the star, where is the point?
 
  • #32
Drakkith
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The VLT looked for signals from some exoplanet recently. I checked the numbers, we would have been able to detect signals similar to some of our transmissions in the past.
I guess I must be remembering what I read incorrectly then.
 
  • #33
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If (on average) 1 out of 1 billion species develops intelligence on a human level and an average planet with life sees 1 billion species during the lifetime of the star, where is the point?
Our planet will likely experience a lot more species yet, as we are only 60 - 70% of the way through our planet's habitability. However the rate of mass extinctions is decreasing as solar system debris is swept up, which stymies the rate of new species production.

I would like to point out that the Earth is likely an extreme example of life. Microbial life is almost stupidly abundant, hardy, and quick to form (based on geological records) - its animal life that's the hail mary. Maybe saying 'every planet that sustains complex animal life' instead of just 'any planet with life' is a more accurate estimate.
 
  • #34
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The first supernova/hypernova probably did not originate until the universe was about 500 million years old. Given life as we can imagine it demands an abundance of metallicity, it appears unlikely it could have originated less than ~ 5 billion years after the big bang - or between 8 - 9 billion years ago.
Chronos, I strongly disagree. Since the question is how soon life COULD form, we can make a series of best-case scenario assumptions and remain within the bounds of plausibility considering the number of star clusters in the universe as a sample size.

We do not need to wait for galaxies to form, we can consider any cluster of gas capable of star formation. Star formation could have occurred as soon as 100 million years after the Big Bang (0). Supermassive stars can fuse their supply of nuclear fuel in as little as 1 million years or less (1). We could have a run of several generations of supermassive stars in less than 50 million years years, including time for dispersal and reformation of metallic elements. Within this one cluster there would be a substantially metal-rich material.

Within this cluster, shockwave compression from aformentioned supernovas could produce a spinning protoplanetary disc in as little as 100,000 years (2). For the next 50 million years our star is in the T-Tauri phase, however during this period planetisimals are forming, and recent work suggests most of the amino acids for life formed during this period as well (3). In fact, before the sun has even entered the main sequence, by 10 million years after protoplanetary disc accretion the outer planets have already formed their rocky cores (4).

Therefore we already have the necessary conditions for life by roughly 160 million years after universe initiation. Rocky cores with internal heating by isotope decay, deposition of amino acids, and abundance of water ice which can be melted by geothermal heat. A lower bound estimate for how long is takes life to form in these conditions is a surprising 10 million years (Millar and Lazcano; 5).

Therefore the absolute lower bound estimate for the formation of microbial / RNA life is 170 million years after the Big Bang.

References:
0. http://www.scientificamerican.com/article.cfm?id=the-first-stars-in-the-un
1. http://astronomy.nmsu.edu/tharriso/ast110/class19.html
2. Thierry Montmerle, Jean-Charles Augereau, Marc Chaussidon (2006). "Solar System Formation and Early Evolution: the First 100 Million Years". Earth, Moon, and Planets (Spinger) 98 (1–4): 39–95
3. Moskowitz, Clara (29 March 2012). "Life's Building Blocks May Have Formed in Dust Around Young Sun"
4. Douglas N. C. Lin (May 2008). "The Genesis of Planets" (fee required). Scientific American 298 (5): 50–59.
5. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980209932_1998078963.pdf
 
  • #35
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@Drakkith: Sorry, it was not the the VLT (that would be optical/infrared anyway), I confused it with VLBI - radio waves.

From our results we place an upper limit of 7 MW/Hz on the power output of any isotropic emitter located in the Gliese 581 system, within this frequency range.
Gliese 581 is ~20 light years away.

As comparison, the Arecibo message had 1MW with ~1 Hz bandwidth, but not isotropic. This reduces the required power a lot.

There were two transmissions directed at Gliese 581, but I could not find power values for them.


H2Bro said:
I would like to point out that the Earth is likely an extreme example of life. Microbial life is almost stupidly abundant, hardy, and quick to form (based on geological records) - its animal life that's the hail mary. Maybe saying 'every planet that sustains complex animal life' instead of just 'any planet with life' is a more accurate estimate.
It does not matter which values you use as comparison. The fact that just one species on earth developed human-scale intelligence is not an argument against the probability that human-scale intelligence evolves. That probability could be everything from "extremely small" to "something around 1/2" without any evidence to distinguish between those numbers.
 
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  • #36
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The Aricebo message has an effective isotropic radiated power of 20 TW and a bandwidth of 5 MHz (well, that's the narrowest it goes; I don't know what they actually used). That's 4 MW/Hz.

Alpha Centauri is 4.6 times closer, so the signal would be 20x stronger, or about 100 MW/Hz equivalent. No problem to see with a sensitivity of 7.
 
  • #37
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5 MHz bandwidth?
Wikipedia said:
transmitted at a frequency of 2380 MHz and modulated by shifting the frequency by 10 Hz
Source
On November 16, 1974, the Arecibo Observatory transmitted at 2380 MHz at an effective bandwidth of 10 Hz a message directed at the globular cluster M13.
I think there is a good safety margin, if the receiver listens at the whole frequency band or the communication is coordinated.

10 Hz instead of 5 MHz increases the power (per frequency range) by a factor of nearly 10^6, which corresponds to an increased range of a factor of 10^3 (20000 ly instead of 20) - or a factor of 10^6 (?) in bit rate.
 
  • #38
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Yes, the width is 5 MHz. The modulation rate is 10 MHz.
 
  • #39
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Where does that number come from?
With a width of 5 MHz, I would imagine that it is hard to detect a shift of 10 Hz (not MHz!).
 

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